Fleets of vehicles with specific tasks, such as school buses, garbage trucks, and delivery vehicles, often need to be tracked to ensure that, among other things, their drivers are performing their appointed tasks. However, such tracking need not be real-time tracking as the operators of these fleets only need to know that each vehicle has performed its rounds and that specific events, such as the lowering of gates on school buses or the opening and closing of delivery doors on delivery trucks, have properly occurred.
So called telematics devices are widely used to service the above needs. Current telematics technology for tracking vehicle fleets commonly use Global Navigation Satellite System (GNSS) receivers coupled with two way communications systems such as cellular radio or two way mobile radios to periodically transmit location and telemetry data to a remote telematic host computer that is further connected to the Internet. This telematics data is stored in a database within the telematics host computer and is provided to client software executing on remote work stations via the Internet. This data can be used to generate reports and presentations of the movements and activities of the vehicles on a graphical display.
These telematics devices may include subsystems which allow for the transmission of telemetry data to record telematics “events” related to vehicle hardware and/or “smart” GNSS events generated by algorithms designed to minimize outbound interrogation requests for data.
Two way mobile radio networks have considerably less bandwidth compared to cellular radio networks, so that minimizing data to be transmitted by way of the two-way radio is important. This problem is exacerbated by the time required by the network to coordinate and manage communication transactions. For example, in a typical trunked radio network, the data transmission time for a single GNSS location report might amount to approximately 150 ms, but the entire transmission time may approach the larger part of a second because of the call setup overhead.
Two way radio networks provide certain particular advantages for specific applications relative to cellular radio networks, including lower recurring costs, inherent one-to-many communications, and significantly better immunity to overload failures in emergency situations.
The requirement to track fleets of vehicles and communicate telemetry data is an increasingly common requirement. This has led to higher use of the limited data bandwidth on two-way radio networks, resulting in a need to reduce the amount of data transmitted for this purpose.
One common partial solution to this, for modern digital radio networks, is to increase the available data bandwidth through the addition of one or more channels dedicated solely to data communications. However, frequent location reports (e.g. every few seconds), or the aggregate of location reports from a large fleet of vehicles, even with low report rates, can fully occupy the entire bandwidth of such additional data channels. Also, the requirement for frequent changeovers from voice to data transmissions for transmission of location data significantly complicates the requirement that each radio be continuously available for voice communication.
Prior art systems use a number of techniques which can decrease the data bandwidth used for the transmission of locations and telemetry reports. One such system provides for transmission of multiple location reports in a single transmission so as to reduce the average call set-up time, with additional data manipulation techniques to minimize the number of bits transmitted.
However, each of these techniques has its own limitations and drawbacks.
From the above, there is therefore a need for methods that address the issues associated with two-way radio data transmissions, especially with respect to the frequent reporting of data from vehicle fleets.